Tail-directed behaviour in pigs - relation to tail posture and tail lesion
Tail-biting in pigs affects the health and welfare of the animals. Different indicators, such as the tail posture, can be used to detect tail-biting at an early stage. The aim of this study was to investigate the effect of tail-directed behaviour, differentiating between tail-biting and tail-in-mouth behaviour, on tail lesions and tail posture of 6 groups of 24 undocked piglets in identical pens using detailed behavioural observations of the four days (t-1 to t-4) before a tail-biting outbreak. Tail lesions were scored twice a week. The tail posture and the tail-directed behaviour were recorded using video observation. Generalised linear mixed models were used separately for tail-biting and tail-in-mouth behaviour to test the influence of the number of receiving (RT) or performing (PT) tail-directed behaviour on the multinomial tail lesions (0: no tail lesion, 1: superficial tail lesion, 2: small or large tail lesion) and to test the influence of RT and PT and the fixed effects of pen (1-6), day (t-1 to t-4), hour (10:00 h – 17:00 h), location (at the trough, not at the trough) and receiver (received tail-directed behaviour in the previous 20 min, received no tail-directed behaviour in the previous 20 min) on the binary tail posture (0: raised tail posture, 1: lowered tail posture). For the tail-biting behaviour dataset, the results showed that piglets with a higher RT had significantly more severe tail lesions (p < 0.05). For the tail-in-mouth behaviour dataset, RT had a significant but reversed effect on tail lesion (p < 0.05). Tail-in-mouth behaviour had no significant influence on tail posture. The probability of a lowered tail posture was significantly higher for piglets that had been tail-bitten in the previous 20 min compared to piglets that had not been tail-bitten (p < 0.05). With an added time offset between the tail-biting behaviour observation and the tail posture observation, the effect of being tail-bitten was still significant for the time offsets of 20–60 min and 100 min (p < 0.05). The day and position in the pen had a significant effect on tail posture as well (p < 0.05). Thus, tail-biting influenced the tail posture and the lasting effect facilitates the use of the tail posture as an indicator for tail-biting.